You can put this solution on YOUR website! how to solve trigonometric identities? what are common step in all soutions
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You don't solve them.
You're given and equation and you prove it is or isn't an identity.
Common steps are substitutions of accepted identities.
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A weak point of most identity problems is that what you're allowed to use is not specified.
Most know that sin^2 + cos^2 = 1
But, can you use sin(3x) = 3sin(x) - 4sin^3(x) ?? Some ppl know it, some don't.